Bitzer Johannes, Otterbach Steffen, Thangavel Kavipriya, Kultaeva Anastasia, Schmid Rochus, Pöppl Andreas, Kleist Wolfgang
Faculty of Chemistry and Biochemistry, Industrial Chemistry - Nanostructured Catalyst Materials, Ruhr University Bochum, Universitätsstraße 150, 44801, Bochum, Germany.
Institute for Chemical Technology and Polymer Chemistry, Karlsruhe Institute of Technology, Engesserstr. 18/ 20, 76131, Karlsruhe, Germany.
Chemistry. 2020 May 4;26(25):5667-5675. doi: 10.1002/chem.201905596. Epub 2020 Mar 11.
Metal-organic frameworks containing multiple metals distributed over crystallographically equivalent framework positions (mixed-metal MOFs) represent an interesting class of materials, since the close vicinity of isolated metal centers often gives rise to synergistic effects. However, appropriate characterization techniques for detailed investigations of these mixed-metal metal-organic framework materials, particularly addressing the distribution of metals within the lattice, are rarely available. The synthesis of mixed-metal FeCuBTC materials in direct syntheses proved to be difficult and only a thorough characterization using various techniques, like powder X-ray diffraction, X-ray absorption spectroscopy and electron paramagnetic resonance spectroscopy, unambiguously evidenced the formation of a mixed-metal FeCuBTC material with HKUST-1 structure, which contained bimetallic Fe-Cu paddlewheels as well as monometallic Cu-Cu and Fe-Fe units under optimized synthesis conditions. The in-depth characterization showed that other synthetic procedures led to impurities, which contained the majority of the applied iron and were impossible or difficult to identify using solely standard characterization techniques. Therefore, this study shows the necessity to characterize mixed-metal MOFs extensively to unambiguously prove the incorporation of both metals at the desired positions. The controlled positioning of metal centers in mixed-metal metal-organic framework materials and the thorough characterization thereof is particularly important to derive structure-property or structure-activity correlations.
包含分布在晶体学等效骨架位置上的多种金属的金属有机框架（混合金属金属有机框架）代表了一类有趣的材料，因为孤立金属中心的紧密相邻常常会产生协同效应。然而，用于详细研究这些混合金属金属有机框架材料，特别是解决晶格中金属分布问题的合适表征技术却很少。直接合成混合金属FeCuBTC材料被证明是困难的，只有使用各种技术进行全面表征，如粉末X射线衍射、X射线吸收光谱和电子顺磁共振光谱，才能明确证明在优化合成条件下形成了具有HKUST-1结构的混合金属FeCuBTC材料，其中包含双金属Fe-Cu桨轮以及单金属Cu-Cu和Fe-Fe单元。深入表征表明，其他合成方法会导致杂质产生，这些杂质包含了大部分添加的铁，仅使用标准表征技术很难或无法识别。因此，本研究表明有必要对混合金属金属有机框架进行广泛表征，以明确证明两种金属都掺入到了所需位置。在混合金属金属有机框架材料中对金属中心进行可控定位并对其进行全面表征，对于推导结构-性质或结构-活性关系尤为重要。
